1. Field of the Invention
The present invention relates to a gas heat pump type of air conditioning system that drives a refrigerant compressor using a gas engine and when performing a heating operation uses exhaust gas from the gas engine as the heating source for a liquid coolant, and particularly to a multiform gas heat pump type of air conditioning system that is provided with a plurality of indoor units and allows a selection to be made between all units performing a cooling operation, all units performing a heating operation, and a combination of simultaneous heating and cooling operations and allows the subsequent switching of the units to the selected option.
2. Description of the Related Art
An air conditioning system that performs air conditioning operations such as heating and cooling using a heat pump is provided with a refrigerant circuit that includes elements such as an indoor heat exchanger, a compressor, an outdoor heat exchanger, and a diaphragm mechanism and the like. Indoor heating and cooling are achieved by the indoor heat exchanger and the outdoor heat exchanger performing heat exchange between air inside a building (referred to below as “indoor air”) and outdoor air as refrigerant circulates around this circuit. In some cases, a refrigerant heater that directly heats the refrigerant itself is added to the refrigerant circuit in order that the system does not have to rely solely on the receiving of heat from the refrigerant by the outdoor heat exchanger (when performing a heating operation).
In recent years, power sources for the compressor provided on the above described refrigerant circuit have been developed that use a gas engine instead of an electric motor. Air conditioning systems that use this gas engine are commonly known as gas heat pump type air conditioning systems (abbreviated below to GHP systems). In these GHP systems, because town gas, which is comparatively inexpensive, can be used as fuel, running costs are reduced in comparison with air conditioning systems having compressors that use electric motors (abbreviated below to EHP systems). Accordingly, the advantage to a user is that lower costs become possible.
Moreover, in a the GHP system, when the system is performing the heating operation, for example, if high temperature exhaust gas discharged from the gas engine and the heat from cooling water used to cool the engine (known as waste or exhaust heat) are used as heating sources for the refrigerant, then an excellent heating effect can be obtained and the energy utilization efficiency increased in comparison with the EHP system. In such cases, the energy utilization efficiency of the GHP system is approximately 1.2 to 1.5 times greater than that of the EHP system. By introducing this type of mechanism, the need to install a special apparatus such as the above described refrigerant heater or the like on the refrigerant circuit is done away with.
In addition, when an operation to remove frost and the like (known as a defrosting operation), which is necessary when the system is performing the heating operation, are performed for the outdoor heat exchanger. In the GHP system, this can be carried out using waste heat from the gas engine. Commonly, when performing the defrosting operation in the EHP system, the heating operation is stopped and the cooling operation is temporarily performed so as to remove frost from the outdoor heat exchanger. As a result, cold air is blown into the room causing a lowering of the comfort level of the indoor environment. In contrast, in the GHP system, because continuous operation is possible for the reasons described above, the problem as described above that has caused in the EHP system does not materialize.
On the other hand, in the EHP system, systems known as multiform systems have been developed. In these multiform systems, it is possible to prepare a plurality of indoor units, place each indoor unit in one of a plurality of various spaces that are to be air conditioned, and cool all of the spaces (i.e., corresponding to the total number of indoor units) or a part of the spaces, or heat all of the spaces (i.e., corresponding to the total number of indoor units) or a part of the spaces. In addition, it is possible to simultaneously perform either the cooling operation, the heating operation, or suspend operations in each space to be air conditioned or for each indoor unit. This type of EHP systems are disclosed in, for example, Japanese Unexamined Patent Application, First Publication Nos. L-247967, 7-43042, and 9-60994.
Accordingly, the application of the same type of multiform system that is used in the EHP system is desired for indoor units of the GHP system that has the numerous advantages as described above.
When the multiform system is applied to the GHP system, it is necessary to match the condensing performance and evaporation performance of outdoor heat exchangers provided in outdoor units with the wide range of requirements that correspond to the operating state of each indoor unit. For example, when the main operation being performed is cooling operation, the condensation performance sought from the outdoor heat exchanger functioning as a condenser changes greatly in accordance with the combination of the number of indoor units currently operating as coolers and the number of indoor units currently operating as heaters. Therefore, a low cost system that can easily demonstrate a condensing performance and evaporation performance that match such requirements is desired.
FIG. 16 is a Mollier diagram showing a refrigeration cycle of an air conditioning system. When the system is performing the cooling operation, the area between i1 and i2 in the diagram is the cooling performance (i.e., evaporation) of an indoor heat exchanger. In order to obtain this cooling performance, it is necessary to obtain the condensing performance between i3 to i1 from the outdoor heat exchanger. However, when a mixture of cooling and heating operations are being performed respectively by a plurality of indoor units, because the heating (i.e., condensing) performance between i4 and i1 is obtained from the small number of indoor heat exchangers that are performing the cooling operation, it is sufficient if a condensing performance corresponding to the area between i3 and i4 is provided by the outdoor heat exchanger. Namely, the cooling performance between i1 and i2 and the heating performance between i4 and i1 are values that change in accordance with the operating state selected by the user. Therefore, the condensing performance required from the outdoor heat exchanger also changes greatly in accordance with this operating state.
When the system is mainly performing the heating operation, the evaporation performance obtained from the small number of indoor heat exchangers that are performing the cooling operation and the condensing performance obtained from the majority of heat exchangers performing the heating operation also change in accordance with the operating state selected by the user. Therefore, the evaporation performance required from the outdoor heat exchanger functioning as an evaporator also changes greatly in accordance with this operating state. Note that, during the heating operation, for example, if engine cooling water is supplied from the gas engine to a water heat exchanger and waste heat from the gas engine is used, then it is possible to supplement the evaporation performance of the outdoor heat exchanger functioning as the evaporator.
Furthermore, when the multiform system is used in the GHP system, if the system is performing the heating operation when outside temperatures are low, moisture in the air sometimes forms as frost on the surface of the outdoor heat exchanger functioning as the evaporator. As a result, the heat exchanging ability of the outdoor heat exchanger decreases and the refrigerant cannot be sufficiently evaporated, and the heating performance of the system deteriorates. To counter this type of frost formation in the outdoor heat exchanger, in a conventional system, a continuous heating operation is made possible by performing a defrosting operation using waste heat from the engine. However, this cannot prevent variations in the heating abilities caused by the frost formation. Therefore, in the multiform gas heat pump type of air conditioning system, the heat exchanger is desired that enables the refrigerant to be evaporated efficiently over a wide range of temperatures with no frost formation when performing the heating operation when outside temperatures are low.
Moreover, when the multiform system is used in the GHP system, in order to ensure stable operating efficiency from the compressor, it is necessary to provide a suitable degree of superheat (approximately 5° C. to 10° C.) to the gas refrigerant that is taken in. However, because it is difficult for sufficient heat to be obtained from the outside air by the outdoor heat exchanger functioning as the evaporator when the outside temperature is low, the necessary degree of superheat cannot be provided to the refrigerant. As a result, the refrigerant is supplied to the compressor still in the form of a two-phase gas and liquid, and the performance of the system deteriorates. In addition, when the system performs the heating operation in low outside temperatures like this, not only is it not possible to obtain a sufficient heating performance, but also the coefficient of performance (COP) is reduced, and measures to counter this are desired.
Furthermore, when the multiform system is used in a GHP system, when the outdoor heat exchanger is separated into a plurality of units that are connected together in parallel, and a refrigerant supply switching means is provided to control the flow of refrigerant to each separate outdoor heat exchanger portion, there are cases when the operation of the separate outdoor heat exchangers is suspended due to the operating state of the indoor units. In the outdoor heat exchanger whose operation is suspended, the liquefied refrigerant due to the relationship between the outside temperature and the refrigerant saturation temperature may accumulates in the outdoor heat exchanger. If this phenomenon occurs, there is an insufficient amount of refrigerant circulating in the refrigeration cycle and, as a result, there is a possibility of the problem arising that the necessary cooling and heating performances cannot be obtained. Therefore, in the multiform gas heat pump type of air conditioning system in which the outdoor heat exchangers are separated into a plurality of units, it is necessary to recover the liquefied refrigerant accumulated in the outdoor heat exchangers whose operations have been suspended.
The present invention was conceived in view of each of the above circumstances and it is a first object thereof to provide a multiform gas heat pump type of air conditioning system that is provided with a plurality of indoor units and that is provided with an inexpensive system capable of easily changing performance in response to required variations in condensing performance and vaporization performance in an outdoor heat exchanger in accordance with the operating state of a multiform system that is capable of performing both cooling and heating operations.
It is a second object of the present invention to provide a multiform gas heat pump type of air conditioning system capable of evaporating the refrigerant with no frost formation and giving excellent heating performance even when performing the heating operation when the outside temperature is low.
It is a third object of the present invention to provide a multiform gas heat pump type of air conditioning system capable of providing the desired degree of superheat to gas refrigerant taken into a compressor even when performing the heating operation when the outside temperature is low.
It is a fourth object of the present invention to provide a multiform gas heat pump type of air conditioning system capable of recovering liquefied refrigerant accumulated inside an outdoor heat exchanger whose operation is temporarily suspended and prevent the insufficiency of the refrigerant.